Field of the Invention
The present invention relates to a traveling screen system, having a multiplicity of support and guide rollers, by way of which traveling screen is guided. A device is provided for scanning the transverse position of the traveling screen and a device for adjusting the angular position of at least one of the support and guide rollers. The latter device is supported on one side on a displaceable bearing block. Between the control device for the bearing block of the displaceable roller, which bearing block is disposed on a carriage, and the scanning device, a coupling is provided by which a return of the control motion of the roller toward the scanning device is effected.
Prior art traveling screen systems, which are used in the paper industry, for instance, have many rollers over which a traveling screen is guided. In a traveling screen system that is one of the components of a system for creating a web of paper, squeegee strips and suction devices are also located between the rollers. At the beginning of the traveling screen, a liquid paper pulp is sprayed onto it. Over the course of the traveling screen and its direction of motion, the water contained in the paper pulp passes through the traveling screen, is removed from the underside of the traveling screen by the squeegee strips, and is aspirated away by the suction devices. At the end of the system, a paper web is separated from the traveling screen; the web is then rolled, surface-treated and cut.
For a proper sequence of operation, it is necessary to assure that the traveling screen maintain its direction of motion in the longitudinal direction of the traveling screen system. If any deviation in the direction of motion of the traveling screen occurs, provisions for controlling the traveling screen must be taken, which comprise slightly pivoting the angular position of at least one of the rollers whose pivot axes form a right angle with the longitudinal direction of the traveling screen system. By means of this kind of change in the angular position of at least one of the rollers, it is true that the traveling screen is adjusted slightly transversely to the longitudinal direction of the traveling screen system, but the direction of motion of the traveling screen system is corrected so that it again runs in the longitudinal direction of the traveling screen system.
To detect any deviation in the direction of motion of the traveling screen, it has become known in the art to provide a scanner laterally of the traveling screen. If any change in the direction of motion of the traveling screen occurs, causing one of the side edges of the traveling screen to migrate laterally and exceed a predetermined limit value, then the scanner responds and trips a control event. The control event comprises adjusting the angular position of at least one roller assigned to the scanner. To that end, one of the two bearing blocks of this roller is supported on a carriage, with which a pneumatic or hydraulic control piston is associated. A valve which is controlled by the scanner is located in the control circuit of the control piston. As soon as the scanner, as a consequence of the lateral migration of the traveling screen, responds, the valve in the control circuit is controlled by the scanner in such a way that the bearing block of the roller is displaced. This changes the angular orientation of the roller and the desired correction in the direction of motion of the traveling screen is brought about.
In such control events, however, there is the further requirement of avoiding overcorrections. The reason why overcorrections can be caused is that, as noted above, while a deviation in the direction of motion of the traveling screen from the longitudinal direction of the traveling screen system is to be prevented, nevertheless at the same time a lateral offset of the traveling screen is intended to be allowable, since by means of it irregularities in the traveling screen can be taken into account. If accordingly the control of the angular position of at least one roller is derived solely from the lateral deviation of the traveling screen, then this would lead to an extensive pivoting of the roller, that is to the afore-mentioned overcorrection. To avoid such overcorrections, it has also become known in the art to provide a so-called return guide. This is a device by which, as a result of the change in the angular position of the roller, an adjustment of the control valve counter to the adjustment effected by the scanner is brought about. Thus by means of the return guide, the change in angular position of the at least one adjustable roller effected by the scanner is reduced.
Prior art return guides of this kind have a control rod, which are hinged on the one hand on the displaceable bearing block for the roller and on the other on a carrier for the control valve. As soon as the bearing block is adjusted, an adjustment of the carrier for the control valve also occurs, as a result of which the desired effect of reduction of the controlling variable is attained.
Such prior art devices for return guidance, which include a control rod, are however not capable of meeting the demands or spatial conditions, because they dictate that the scanner and the control device for the bearing block be located directly side by side. This in turn creates the requirement that the traveling screen system be disposed such that the space required for the side-by-side scanner and control device is available. It is often difficult to meet this requirement however, because of spatial conditions.